Stop valves, in particular, ball valves or stop cocks, in particular ball cocks, are used to selectively stop or allow a hydraulic flow. The valves are operated typically by a lever that can be rotated by 90°. In many cases, in the stopped state, a pressure difference builds up between the connection sides of the stop valve, whereupon, when the stop cock is opened, the hydraulic system tries to reach a pressure balance, which is associated with an abrupt, rapid step-wise increase in hydraulic flow. These step-wise changes are often undesired. Particularly in the case of agricultural machines, such as, e.g., tractors or harvesting machines, this pressure-balancing process in hydraulic suspension systems causes a quick, jerk-like motion of the suspension cylinder and thus also of the chassis and the tools installed on the chassis. The higher the pressure difference was in the stopped state, the greater is the movement.
Typically, stop valves can be opened in one pull, so that the complete opening cross section is freed directly. Indeed, the operator can try to open the stop valve in increments, but this is often possible only with much difficulty, especially due to high opening forces and the breaking away of the stop valve slide known as the stick-slip effect and rarely can be reproduced reliably. For this reason, usually unintentionally, a relatively large cross section is immediately opened, whereupon pressure equalization or pressure balance is achieved in sudden bursts and with the negative consequences named above.